Time discriminator



Nov. 5, 1957 R. E. LYON TIME DISCRIMINATOR Filed oct. 5, 1954 4% awr/yf Ku ma;

,Parafia/5f faz 74a! War/afg' www rlME DrscRn/uNAroR Royal E. Lyon, Van Nuys, Calif., assiguor to Hughes Aircraft Company, Culver City, Calif., acorporation of Delaware This invention relates to time discriminators, and more particularly to a time discriminator of the type which can produce a D.C. voltage whose polarity is representative of the phase relationship between a signal pulse and a reference voltage.

`In certain applications, the operation of a device is controlled by the output of a time discriminator circuit which is sensitive to the phase relationship between an error indicating signal pulse and an A.C. reference voltage. Such a time discriminator -is characterized by a positive D.C. output voltage when the signal pulse occurs during the positive half cycle ofthe reference voltage, a negative D.C. voltage when the signal pulse occurs during the negative half cycleA of the reference voltage, and zero output voltage when the signal pulse occurs at the zero degree or 180 point.

Heretofore,.to obtain a predetermined D.C. output voltage from a time discriminator, a reference signal'having a relatively high peak-to-peak voltage amplitude was necessary;` forexample, where `servo motor required a minimum driving voltage of i 50 volts D.C., a reference voltage having a minimumpeak-to-peak amplitude of 100 volts might beunecessary to obtain this D.C. voltage. However, it maybe desired Vto obtain the desired resultsl with a much smaller reference signal. For example, Vthe miniaturizing of the electronic components comprising such a servo system might entail the use of a lower'supply voltage for a reference voltage generator and time Ydiscriminator `circuit because of heat dissipation and other problems attendant Vwith miniaturization, and yet the minimum required output voltage from the discriminator would remain the same.

It is ka primary object of this invention to provide a phase sensitive time discriminator that produces a D.C. voltage of predetermined amplitude with a lower peakto-peak amplitude reference voltage than isV possible with prior art time discriminators.

It is another object of this invention to provide a time discriminator to produce a D.C. output voltage whose polarity is representative ,of the phase relationship between a signal pulse and a reference voltage, wherein the amplitude of aninput reference voltage is no greater than the D.C. output voltage.

.The present in vention` provides an improved time discriminator that produces a predetermined D.C. output voltage with a reference voltage having a peak-to-peak amplitude of approximately one-half of the amplitude that was heretofore necessary. The novel time discrim- United States Patent inator comprises a positive gating circuit and a negative gating circuit, the output of both circuits being coupled to a D.C. voltage developing circuit. A positive and a negative clamping circuit are coupled to the input circuit of the positive and negative gating circuits, respectively. A cathode follower couples the D.C. output from the storage capacitor to both clamping circuits to cause the input circuit for each gating circuit to be clamped to the potential of the D.C. output voltage.

The novel Vfeatures which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection With the accompanying drawing in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention. Referring to the drawing, the single figure is a schematic diagram of a time discriminator in accordance with this invention.

Referring to the drawing, a conventional time discriminator comprises a positive and a negative gating circuit. The positive gating circuit includes an input coupling network which comprises a capacitor 10 connected to a grounded resistor 11 and to an electron tube 13 having a cathode 14, a control grid 15 and an anode 16. Anode 16 is connected to the common connection of capacitor 10 and resistor 11. An RC bias circuit for control grid 15, provided by a shunt connected capacitor 18 and resistor 19, is connected in series with the secondary winding 20 of a transformer 21, between control grid 15 and cathode 14. Y

The negative gating circuit also includes an input coupling network comprising. a'capacitor 22 connected to a grounded resistor 23 and to an electron tube 24 having a cathode 25, acontrol grid 26 and an anode 27. Cathode 25 is connected to the common connection of capacitor 22 and resistor 23. An RC bias circuit for electron tube V2,4, provided by a shunt connected capacitor ZSand resistor 29, is connected between control grid 26 and one end of another secondary winding 30 of the transformer. f

-A reversible D.C. voltage developing means is provided by connecting the anode 27 of electron tube 24 and the cathodey 14 of electron'tube 13 to a storage capacitor 35.

Capacitors 10 and 22 are Vcoupled to a reference signal source (not shown) which develops a suitable reference signal, such as a square wave. Signal or gating pulses are applied to the primary winding 36 of transformer 21 to be applied to the control grids 15, 26 of tubes 13, 24. If the signal pulses coincide with the positive half of the reference signal, tube 13 conducts to apply a. positive charge across capacitor 35; if -the signal pulses coincide with the negative half of the reference signal, tube'24 conducts to result in a negative charge across. capacitor 35. Y 1

The novel improvement of this invention comprises positive and V.negative-clamping circuits and a feedback circuit. The positive clamping circuit includes an electronic voltage responsive switch, such as diode 40, having a cathode 41 and an anode 42, and a capacitor 10 and resistor 11. Cathode 41 is connected to the common connection of capacitor 10, resistor 11 and the anode 16 of tube 13. The negative 4clamping circuit includes a second electronic voltage responsive switch, such as diode circuit consists of an'electron discharge device, Vsuch as, v an electron tube 50, having a cathode 51, a control grid 52-and an anode `53. Anode 53 iskconnected-to a source of positive voltage, B+, control grid 52 is connected to capacitor 35, and cathode 51 is serially connected by a resistor 55 to a source of negative voltage, B. Cathode 51 is further connected to the common connection of the cathode of diode 45 and the anode of diode 40. How the above described circuit operates will now be more fully explained.

Normally electron tubes 13 and 24 are biased below cut-off, preventing conduction when the positive half of the square wave reference voltage is impressed by means of capacitor onto anode 16, or when the negative half of the reference voltage is impressed onto cathode 24 by means of capacitor 2i). Assuming the signal pulse, which must always be positive with the bias means shown in the preferred embodiment, occurs during the positive half cycle of the square wave, it is applied by transformer 21 to the control grids 15 and 26 of tubes 13 and 23, respectively, and is of suicient amplitude to raise the bias of both tubes above cut-olf. However, only electron tube 13 will conduct during the positive half cycle of the square wave; in conducting it will charge capacitor 35. The voltage at cathode 51 will follow the change in charge across capacitor 35. The positive increase in voltage on cathode 51 is coupled to the anode 42 of clamping diode 40.

So long as the signal input pulse occurs lduring the positive half cycle of the reference voltage, the voltage on the grid side of capacitor will increase in a posi- .tive direction, and the voltage on the cathode of electron tube 50 will continue to follow until its value becomes greater than the peak value of the reference voltage. When this occurs, the anode 42 of diode 40 will be more positive than its cathode and electron tube will conduct. The electron ow will be from ground through resistor 11, electron tube 40 and electron tube 50. The current tlow through resistor 11 causes the plate of capacitor 10 that is connected to the cathode 41 of electron tube 40 to become more positive until it reaches the anode potential.

The RC time constant of capacitor 10 and resistor 11 is made sufficiently long so that the cathode of diode 40 is maintained approximately at its anode potential until the next positive half cycle occurs. Every time thereafter that electron tube 13 conducts, the voltage on the grid side of capacitor 35 becomes more positive, and this positive increase in voltage is transmitted by the cathode of electron tube to the anode of electron tube 40. The cathode of electron tube .40 rises `to the anode potential and is held at approximately this poten-tial by virtue of the long RC time constant 4of capacitor 10 and resistor 11, as heretofore explained.

The limiting value of the charge on capacitor 35 depends on the operating characteristics of electron tube 24. So long as the positive voltage on the grid side of capacitor 35 does not cause electron tube 24 to conduct, the voltage across capacitor 35 may be increased. The net effect is that the anode of electron tube 13 is clamped to the D.-C. potential on the cathode of electron tube 50. The output voltage on cathode 51 will, therefore, be onehalf the peak-to-peak value of the reference voltage plus approximately the voltage across capacitor 3S. It follows that a lower amplitude reference voltage can be provided to obtain a predetermined constant amplitude of D.C. output voltage.

When the signal pulse occurs during the negative half cycle of the reference voltage, the identical operation occurs except tha-t electron tube 24 is gated during the negative half of the reference voltage; capacitor 35 discharges, and electron tube 45 cooperates with capacitor 22 and resistor 23 to provide the clamping circuit.

No oscillations will occur by the use of the feedback circuit just described because the gain of the cathode follower circuit is not greater than unity.

What is claimed as new is:

1. A time discriminator for producing a direct current voltage whose polarity .is representative of the phase relationship between a signal pulse and a reference voltage from a reference generator, comprising: means for developing a direct current voltage in response to and having a polarity dependent upon a voltage being impressed thereon; positive gating means for gating the reference voltage generator to permit the positive amplitude of reference voltage to be coupled to said means for developing a direct current voltage when the signal pulse occurs during the positive half cycle of the reference voltage; negative gating7 means for gating the reference voltage generator to permit the negative amplitude of reference voltage to be coupled to said means for -developing a direct current voltage when the signal pulse occurs during the negative half cycle of the reference voltage; means coupled to said positive gating means for clamping the positive amplitude of reference voltage being coupled to said direct current voltage developing means to the amplitude of the direct current voltage; means coupled to said negative gating means for clamping the negative amplitude of voltage being coupled to said direct current voltage developing means to the amplitude of the direct current voltage; and feedback means for coupling the direct current voltage produced thereby to said positive and negative clamping means.

2. A time discriminator for producing a direct current voltage whose polarity is representative of the phase relationship between a signal pulse and a reference voltage from a reference generator comprising: means for developing a direct current voltage in response to and having a polarity dependent upon the reference voltage being impressed thereon; positive gating means for gating the reference voltage generator to permit the positive amplitude of reference voltage to be coupled to said means for developing a direct current voltage when the signal pulse occurs during the positive half cycle of the reference voltage; negative gating means for gating the reference voltage generator to permit the negative amplitude of reference voltage to be coupled to said means for developing a direct current voltage when the signal pulse occurs during the negative half cycle of the reference voltage; a positive clamping circuit coupled to said positive gating means for clamping the positive amplitude of reference voltage being coupled to said direct current voltage developing means to the amplitude of the direct current voltage, including an electron discharge device; a negative clamping circuit coupled to said negative gating means for clamping the negative amplitude of voltage being coupled to said direct current voltage developing means to the amplitude of the direct current voltage; including an electron discharge device; and means for coupling the direct current voltage developed thereby to said positive and negative clamping circuits, including a third electron discharge device.

3. A time discriminator for producing a direct current voltage 'whose polarity is representative of the phase relationship between a signal pulse and a reference voltage from a reference generator, comprising: means for developing a direct current voltage in response to and having a polarity dependent upon the polarity of the reference voltage being impressed thereon; positive gating means for gating the reference voltage generator to permit the positive amplitude of reference voltage to be coupled to said means for developing a direct current voltage when the signal pulse occurs during the positive half cycle, including a resistance-capacitance input network for coupling the reference voltage to said positive gating means; negative gating means for gating the reference voltage generator to permit the negative amplitude or" reference voltage to be coupled to said means for developing a direct current voltage when the signal pulse occurs during the negative half cycle, including a resistance-capacitance input network for coupling the reference voltage to said negative gating means; a positive clamping circuit, including a first voltage responsive switch coupled to the resistance-capacitance input network of said positive gating means; a negative clamping circuit, including a second voltage responsive switch coupled to the resistance-capacitance input coupling network of said negative clamping means; and feedback means, including a cathode follower circuit connected between a source of negative voltage and a source of positive voltage for coupling the direct current voltage developed thereby to said positive and negative clamping circuits.

4. In combination with a time discriminator adapted to produce a direct current voltage'representative of the phase relationship between a signal pulse and a reference voltage from a reference voltage generator, wherein the time discriminator includes a direct current voltage developing circuit, a positive gating circuit coupled between the reference generator and the direct current voltage developing circuit, and a negative gating circuit coupled between the reference generator and the direct current voltage developing circuit: a clamping circuit comprising a first voltage-responsive electronic switch coupled to the positive gating circuit, a second voltage-responsive electronic switch coupled to the negative gating circuit, and a feedback circuit comprising a cathode follower circuit coupled between the direct current voltage developing circuit and said first and second voltage-responsive electronic switches, said cathode follower and said first and second voltage responsive switches cooperating to clamp the amplitude of the reference voltage being gated to the potential of the direct current output voltage. 30

S. The combination as dened in claim 4 wherein said first and second voltage responsive electronic switches are unidirectional conductive electronic discharge devices.

6. The combination as dened in claim 4 wherein said rst voltage responsive electronic switch comprises a diode having a cathode and an anode, and said second voltage-responsive electronic switch comprises a second diode having a cathode and an anode, the cathode of ,said first diode being coupled to the positive gating cir- References Cited in the tile of this patent UNITED STATES PATENTS 2,497,693 Shea Feb. 14, 1950 2,515,055 Peterson July 11, 1950 2,521,058 Goldberg Sept. 5, 1950 2,597,886 McCoy May 27, 1952 2,644,887 Wolfe July 7. 1953 .2,683,806 Moody July 13, 1954 2,708,718 Weiss May 17, 1955 

